By using the open circuit voltage analytical model and AMPS, a simulation analysis has been made of the effects of temperature on the properties of a- Si:H/c-Si heterojunction solar cells and its mechanism. The increase of temperature T leads to an increase in the thermal voltage and a decrease in the open-circuit voltage. The fill factor FF increases drastically when T<270 K while remains unchanged when T ≥270 K, with the highest conversion efficiency of a-Si:H/c-Si heterojunction solar cells obtained when T=270 K. When at work under a low temperature, the quantum transport is restricted by the barrier of valence band compensation interface, with S-Shape phenomenon occurring in J-V, thus significantly reducing the filling factor FF.